1. Field of the Invention
The present invention relates generally to an automatic power transmission for an automotive vehicle. More particularly, the invention relates to an automatic power transmission with a subsidiary transmission unit.
2. Description of the Background Art
Japanese Patent First (unexamined) Publication (Tokkal) Showa 58-211920 discloses an automatic power transmission with a subsidiary transmission unit. The disclosed transmission has a primary pressure accumulator for a primary transmission unit mounted on a primary transmission casing and a subsidiary pressure accumulator unit for the subsidiary transmission unit for over-drive speed ratio, mounted on a subsidiary transmission casing. In such prior proposed layout, the subsidiary pressure accumulator is connected to a flow restriction orifice and an one-way check valve so as to assure providing pressure variation characteristics with a predetermined pressure range in which the fluid pressure to be supplied to a friction element in the subsidiary transmission unit increases at smaller rate than that in the other ranges. In the prior proposed construction, the flow restriction orifice and the one-way check valve are provided in a hydraulic control unit which is mounted on the primary transmission casing. Therefore, a long fluid path is needed for connecting the subsidiary pressure accumulator in the subsidiary transmission unit to the flow restriction orifice and the one-way check valve in the hydraulic control unit on the primary transmission casing. Such a fluid path extends both through the primary and the subsidiary transmission casings and has to be connected in a liquid tight fashion at the interface between the primary and subsidiary transmission casings.
This makes the fluid path structure in the transmission casings complicated, causing difficulty in designing. As well, because of the length of the fluid path, a delay in response in the friction element provided in the subsidiary transmission unit is necessarily caused.